Beginning with the romesco, throw all of the ingredients for the sauce into your food processor or blender. Traditionally, it's a bit of a chunky spread, but I prefer mine perfectly smooth and creamy, so I use my Vita-Mix. Blend to your desired consistency, scraping down the sides of the work bowl periodically so that no large chunks are left behind, and set aside. I find it tastes better if you allow it to sit for at least 2 hours before serving, so that the flavors can meld, but it can be eaten right away too.

For the leek topping, slice your thick leek into quarters lengthwise, and then chop it into 1/2-inch pieces. I love the look of rings or half moons, but it's not so graceful to take a bite of crostini and end up with a big loop of leek hanging out of your mouth, so resist the temptation to leave the pieces larger.

Heat up the oil in a sautee pan over medium heat, loosen up the miso paste in it if using, and toss in the chopped leek. Stir every 5 minutes or so for a total of 20 - 25 minutes, until the leek is soften but not completely mushy. Add salt and pepper to taste, and let cool for at least 15 minutes.

Both the sauce and leek topping can be made in advance as well. Just store both in air-tight containers in the fridge for 4 - 5 days, and assemble the crostini just prior to serving.

To put the crostini together, just smear a healthy dollop of the romesco on top of the toasted bread, and spoon about 1 - 2 tablespoons of the sauteed leek over that. Finish with a very light sprinkling of red pepper flakes.